1. Field of the Invention
The present invention relates to a continuous variable valve lift device, in which a valve has simultaneously variable lift time and distance depending on the low-/high-speed operating range of an engine, and more particularly to a continuous variable valve lift device, in which additional components for conducting variable lifting of a valve are minimized, thereby providing a more simple structure.
2. Description of the Related Art
As for an engine, a camshaft is rotated by a rotating force transmitted from a crank shaft, and an intake valve and an exhaust valve are reciprocated up and down with regular timing by cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and then combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power.
In this manner, a series of elements such as a drive cam, a camshaft, a tappet, a rocker arm, etc. for operating the intake and exhaust valves is called a valve train.
In a conventional art, a valve is installed on an intake or exhaust port in a cylinder head through a valve guide. A spring support plate is installed on a cylinder head body. A valve spring is installed between the spring support plate and a spring retainer. A tappet of the valve is installed so as to contact a drive cam.
The ordinary valve train configured in this way repeats the operation in which the drive cam rotates to push the valve tappet to open the valve while compressing the valve spring, and then the valve is closed by a recovery force of the valve spring.
However, this ordinary valve train makes a single degree-of-freedom system motion by motion of the cam, so that it is impossible to change the valve train depending on engine operation conditions such as high-speed and low-speed engine operation conditions.
In order to solve this problem, there have been developed a variety of continuous variable valve lift devices, each of which is adapted to adjust a lift time and a lift distance of the valve according to the engine speed. However, these continuous variable valve lift devices must change positions of the drive cam and the camshaft, so that it is impossible to easily apply them to existing mass-produced engines.
Further, these continuous variable valve lift devices are designed to adjust the lift time of the valve by increasing or decreasing the lift distance of the valve, so that it is impossible to more efficiently adjust the lift time of the valve.
In addition, the continuous variable valve lift devices additionally require a separate variable cam in addition to the drive cam coupled to the camshaft in order to adjust the lift distance and the lift time of the valve, so that they have complicated internal configuration.